In an analysis using a liquid chromatograph, an auto-sampler is used to automatically inject a plurality of samples into a column in a predetermined order. A commonly used technique for auto-samplers is the so-called total volume injection method, in which a predetermined amount of sample is collected from a sample bottle and the entirety of the collected sample is injected into a mobile-phase channel. (For example, refer to Patent Document 1.)
In the process of injecting a sample by the total volume injection method, a predetermined amount of sample is initially suctioned from a sample bottle by using a needle. The suctioned sample is charged into a sample loop (measuring loop) connected to the base end of the needle. Subsequently, the needle is inserted into the sample injection port, while the channel configuration of the sample side is changed by means of a channel-switching valve so that the sample loop will be inserted in the mobile-phase channel extending from the mobile-phase container to the column. As a result, the entire amount of the sample charged in the sample loop is pushed forward by the mobile phase, to be injected into the column.
In such an auto-sampler adopting the total volume injection method, it is necessary to minimize the internal volume of the channel to improve the sample-separating performance. Accordingly, in a conventional auto-sampler, the sample injection port is directly attached to the channel-switching valve without using any pipe or similar connecting element. (Refer to Patent Document 2.)
FIG. 8 shows one example of the configuration of the sample injection port and the channel-switching valve in the aforementioned conventional auto-sampler. The channel-switching valve 4 is, for example, a six-port two-position rotary valve, which has six ports, including the sample injection port 100, arranged at regular intervals in a stator 42 provided in the upper part of a casing 41. The sample injection port 100 is plugged vertically in the stator 42, which has internal channels respectively extending from the ports to a rotor 43 fixed to a shaft 44 within the casing 41. The rotor 43 can be rotated in the state of being thrust onto the lower surface of the stator 42 by a spring 45. The rotor 43 has three arc-shaped grooves carved on the sliding surface as paths for connecting the neighboring ports. Rotating the shaft 44 changes the connection state of these ports and thereby alters the channel configuration.
As shown in FIG. 9, the sample injection port 100 has an introduction hole 100a penetrating through the center of its body. The upper mouth of the introduction hole 100a is open at the bottom of a female-tapered needle-seal surface 100b. The sample injection port 100 is made of a polyether ether ketone resin, represented by “PEEK” (registered trademark), or similar material. When a needle 9 is inserted in the sample injection port 100, the tapered tip of the needle 9 fits the female-tapered needle-seal surface 100b, thus establishing between them a liquid-tight connection.
Patent Document 1: JP-A H6-148157
Patent Document 2: JP-A 2003-215118
Patent Document 3: Japanese Registered Utility Model No. 3129670